1. Field of the Invention
Embodiments of the present invention generally relate to large area substrate processing systems. More particularly, embodiments of the present invention relate to a bushing for a support pin for large area substrates.
2. Description of the Related Art
Thin film transistors have been made on large area glass substrates or plates for use in monitors, flat panel displays, solar cells, personal digital assistants (PDA), cell phones, and the like. These transistors are made by sequential deposition of various films including amorphous silicon, doped and undoped silicon oxides, and silicon nitride in vacuum chambers. The film deposition may take place in a single deposition chamber, or the substrate being processed may be transferred between multiple deposition chambers.
In large area substrate processing systems, the substrate being processed typically rests on a substrate support, such as a susceptor, situated within the chamber. To facilitate transfer of the substrate between deposition chambers, support pins may extend through an upper surface of the substrate support and may be raised and lowered with respect to the substrate support so that the substrate may be spaced apart from the substrate support. This spacing allows a transfer mechanism, such as a robot blade, to slide underneath and lift the substrate off the substrate support without causing damage to the substrate support or the substrate.
The support pins are typically rigid, vertical posts of fixed height which extend through the substrate support. During processing, the substrate is placed on the support pins and the support pins are lowered in relation to the substrate support, placing the substrate in contact with the substrate support. After film deposition is complete, the support pins may be raised in relation to the substrate support, lifting the substrate from the substrate support.
A conventional support pin may include a holder or bushing, such as a slide bushing or roller bushing, which is designed to provide lateral support to the support pin and to facilitate movement of the support pin through the bushing along an axis perpendicular to the plane of the substrate support. Conventional slide bushings are typically fabricated from materials which have relatively low melting points, such as polytetrafluoroethylene (PTFE). Consequently, these bushings are unsuitable for use in processing environments of greater than about 250° C. Roller bushings, on the other hand, include moving parts, such as bearings and rollers. Consequently, these bushings are expensive to produce and prone to failure. Additionally, roller bushings may contact a support pin at as many as eight points. The resulting friction created between the support pin and the bushing, as well as friction created between moving parts within the bushing, may produce unwanted particles that can contaminate the substrate during processing. These issues are exacerbated by the increasingly high temperatures required for thin film deposition processes. At such temperatures, the thermal expansion of various components may cause increased friction and binding, and materials may reach softening points, leading to deformations which may result in device failure. Bushing failure may lead to broken panels, increased chamber maintenance costs, and decreased throughput due to chamber downtime.